1. Field of the Invention
The present invention relates to an ink jet printing apparatus and an ink jet printing method by which a printing head that can eject ink is used to print an image on a printing medium such as a paper or plastic.
2. Description of the Related Art
At present, ink jet printing apparatuses have been widely used in the copy and facsimile fields due to the improved image quality and the reduced printing time enabled by smaller ink dots.
In order to print an image with a higher resolution and a reduced printing time, nozzles may be arranged with a high density or a long printing head may be used. In this case, an attachment error caused when printing head is arranged with an error and an application error caused when chip is applied in a printing head with an error (chip in which nozzles are provided) for example have a significant influence on an image quality of a printed image. For example, a case is assumed where a printing apparatus using a plurality of printing heads for a multicolor full color printing or the like is structured so that one of the plurality of printing heads is attached to another printing head with an inclination. In this case, dot formed by the inclined printing head is superposed with dot of a neighboring pixel printed by the another printing head, which may cause a risk where a printed image has a degraded appearance quality. When a single printing head is used for a printing operation and when the printing head has an inclination with a level equal to or higher than a certain level, a resultant image may have a degraded appearance quality. In the case of a serial type printing apparatus in particular, boundaries among the respective printing/scanning regions may be conspicuous.
When the printing head has an inclination (i.e., when the nozzle row has an inclination) as described above, a risk may be caused where positions at which ink droplets are adhered (a position at which ink dots are formed) may be displaced to deteriorate a resultant image. One of methods for preventing this is to detect a displacement amount of a dot formation position to control, based on the detection result, a timing at which a printing head ejects ink. Another method is to shift a relation between a position to which a printing head of a serial type printing apparatus is moved in the main scanning direction and printing data for driving the printing head so that the displacement of a dot formation position due to the inclined nozzle row can be corrected. Methods for detecting a displacement amount of a dot formation position include, for example, the one for printing a test pattern such as a ruled line to detect the displacement amount based on the printing result. Another method for detecting a displacement amount of a dot formation position is to detect a displacement amount between dot formed by ink ejected from an end nozzle positioned at one end of a nozzle row and dot formed by ink ejected from an end nozzle positioned at the other end of the nozzle row. This detection method is disclosed, for example, in Japanese Patent Unexamined Publication No. H11-240143.
On the other hand, among the methods for reducing the deterioration of an image appearance quality based on the detection result of the displacement amount as described above, there is a method for changing a timing at which a nozzle of a printing head is driven. Japanese Patent Unexamined Publication No. H07-40551 discloses a method by which a plurality of nozzles arranged in a printing head are divided to a plurality of blocks so that the detection result of a dot displacement amount corresponding to an inclination of the printing head is used as a base for adjusting an order at which the respective blocks are driven (an order at which ink is ejected).
By the way, recent ink jet printing apparatuses in which a printing head can be exchanged by a user have a risk in which the printing head cannot be attached accurately and have another risk in which, whenever a printing head is attached, the printing head may be attached with a different inclination angle. Thus, the operation for correcting the displacement of the dot formation position due to the inclination of the nozzle row as described above may be performed with a higher frequency. Thus, the operation as described above must be easy-to-understand for users.
Furthermore, the method for detecting the displacement amount of the dot formation position disclosed in Japanese Patent Unexamined Publication No. 11-240143 has a problem as described below. Incidentally, this method detects, as described above, a displacement amount between dot formed by ink ejected from an end nozzle positioned at one end of a nozzle row and dot formed by ink ejected from an end nozzle positioned at the other end of the nozzle row.
Specifically, when both of end nozzles at one end and the other end eject ink simultaneously, displacement among dots formed by these inks most reflects an influence by the inclination of the nozzle row. However, these end nozzles in many cases do not eject ink simultaneously. Furthermore, even when these end nozzles eject ink simultaneously, it is difficult to accurately detect the displacement amount of a dot formation position. Specifically, end nozzles positioned at one end and the other end of a nozzle row tend to be influenced, when compared with other nozzles, by water evaporation of ink in the printing head. Thus, when an ink ejecting interval is long, ink ejecting deviation that shifts a direction along which ink is ejected tends to be caused. Furthermore, when an end nozzle and another nozzle collectively eject ink, the end nozzle tends to be influenced by air current caused by the collective ink ejection. This causes a risk where a direction along which ink is ejected from the end nozzle may be shifted.
On the other hand, in the case of the method as described in Japanese Patent Unexamined Publication No. 07-40551 in which a nozzle row is divided to a plurality of blocks to control the respective blocks, a risk may be caused where an extremely large inclination of the nozzle row prevents a minute correction to the predetermined number of divided blocks. For example, when a displacement amount between both end nozzles is large and when a predetermined number of divided blocks is two, correction for significantly improving the image appearance quality is difficult. As described above, a close relation has existed between an inclination of a nozzle row and the number of divided blocks of the nozzle row. However, this relation has been not considered.